The present invention generally relates to the field of damper operators and is particularly adapted for use with multi-bladed air, smoke or fire dampers, said blades being adpated to open and close as a unit and further, said dampers employing a device to actuate the operator in response to excessive temperature increases in the vicinity of the device or in response to remote signals received thereby. Conventionally, such dampers are provided with blade linkages which articulate the blades with respect to the frame so that the blades will move in unison between their open and closed positions therein. It has long been known that such dampers may be operated using cables attached to the blade brackets or blade linkages within the dampers, which cables are normally threaded through a ferrule disposed damper/duct wall to reach an operator motor outside of the duct in which the damper is located. It is also known to bias the blades toward the closed position, as for example, by using springs extended between the damper frame and the blades, and to provide fusible links in the cable portion located within the duct, so that in response to an excessive temperature, the cable will break and the springs cause the blades to move to the closed position, whereupon the passage of fire through the duct will be halted. Similar, arragements have also been used to provide dampers which are intended to move to the open position in response to a selected stimulus and for air dampers wherein the blades are set to normally operate at an intermediate partially opened position.
Alternatively, it is known to operate dampers through a damper operator shaft, the rotation of which through an arc of approximately 90.degree. corresponds to the rotation of the damper blades through 90.degree. between their opened and closed positions. See, for example, the structure and various damper operators disclosed and discussed in my prior issued U.S. Pat. No. 4,113,232, dated Sept. 12, 1978, entitled "Smoke, Fire and Air Control Damper with Stamped Blade".
Motorized operators for use in rotating damper operator shafts through an arc of 90.degree. are also known. One advantage of such operators is that they normally may be controlled from a remote power source to adjust air flow through the damper by rotating the damper blade preselected number of degrees from the closed toward the open position. In most applications this number is normally assumed to correspond to the percentage of air flow through that damper, for example, a 10.degree. movement of the shaft normally corresponds to a 10.degree. opening of the damper which is assumed to establish a corresponding air flow of approximately 10% through the damper. In actuality, however, the relationship between the arc blade opening and the air flow is not linear. In particular, during the initial stages of blade opening, the fairly large pressure drop encountered causes correspondingly greater percentage volumes of air permitted to pass through the damper for a given degree of blade opening. As the damper blades approach their fully opened position, the pressure drop decreases and correspondingly smaller increases in air flow are achieved for a given change on the degree of blade rotation. No damper/operator unit is presently known having air flow characteristics which exhibit a substantially linear relationship between air flow and degree of operator shaft rotation throughout its entire working range. Furthermore, while shaft operated dampers may be preferred in certain instances, such operators are typically difficult and expensive to install, primarily due to the fact that they normally must be installed to the damper and adjusted after that damper has been installed within the duct. Such a requirement makes installation difficult and expensive, often resulting in an improperly aligned damper/operator combinations. This is particularly true when the damper operator must be specifically designed for a particular damper type of structure. This problem would undoubtedly be much simpler if a universal damper operator were available which could be adapted to a wide variety of damper structures with a minimum of effort.